We have purified leucocyte pyrogen, prepared an antibody to it in the goat and are currently attempting to label it with I125. We will use the antibody and the iodinated pyrogen as reagents in a radioimmuno assay which can measure pyrogen levels in living animals. We are also engaged in determining whether antibody blocks the other actions ascribed to leucocyte pyrogen, such as sequestration of iron and zinc in the reticuloendothelial system, and chemotaxis. BIBLIOGRAPHIC REFERENCES: Murphy, P.A. In Principles and Practice of Medicine, (ed.) A. M. Harvey and A. H. Owens, Jr., Chapters 90, 91, 95 & 96, Appleton-Century-Crofts, New York, 19th edition, 1976.